Method of magnifying waveforms on a cathode-ray tube and circuit therefor



June 26, 1956 R L ROPIEQUET ET AL 2,752,527

7 METHOD OF MAGNIF'YING WAVEFORMS ON A CATHQDE-RAY TUBE AND CIRCUITTHEREFOR Filed Aug. 18, 195.3

MAG- NORM SWEEP G EN ERATOR SWEEP GENERATOR IN VEN TORS Rich are LPopz'e q u e Z y G; CJifford H. Moulfon United States Patent Ofifice2,752,527 METHOD or Mironunvmo WAvEFonMs' ON A @A'lIiUDE-RAY TUBE ANDCIRCUIT THERE- FUR Richard L. Ropiequet and (CliifordH. Moulton,Portland,

Oreg'.,. assignors toTelrtronix, Inc., Portland, reg., a corporation ofOregon Application August 18, 1953, Serial No. 374,871 12 Claims. (Cl.315-26) This invention pertains to the magnification of waveforms on acathode-ray tube, and relates particularly to a method and circuit formagnifying any desired portion of a waveform and positioning the same atthe center or any other area of the cathode-ray tube screen.

It is a principal object of thepresent invention to.pro'

vide a method and circuit by which any portion of a Waveform desired tobe analyzed may be magnified to any desired. extent and adjusted to anydesired position on the cathode-ray screen.

Another important object of this invention is the provision of a methodand circuit for positioning a magnified waveform at any desired positionon a cathode-ray tube screen. I

A further important'object' of the present invention is to provide amethod and circuit by which a normal or magnified waveform may bepositioned on a cathode-ray tube screen by means of a single control.

The foregoing and other objects and advantages of the present inventionwill appear from the following detailed description takenin connectionwith the accompanying drawings, in which; t

Figure 1 is a schematic diagram showing one'form' of electricalcircuitry embodyingthe features of the present invention; v

Figure 2 is a schematic diagram of a modified forin of electricalcircuitry" embodying the features of this invention; and h p 7 I vFigure 3isa graph showing the magnification results ofth e circuitsshownin Figures 1 and 2.

Stated broadly, the method and circuit of'the present invention involvesaf feedback network between a sweep generator and theani'plifying'system' preceding the oathode-rayti1lie deflection plates;wherein means isprovided in saidfeedbacknetwork for'v'arying tliegainof'the output amplifier, and' wherein-means is provided ahead of thefeedback networkdor controlling the horizontal positionflonthewaveformon the cathode-ray: tube screen.

R'ef'er'ringto Figure 1'of'thedrawing;thereis shown in block, form a--sweep gener'atorjill) of any conventional designwell lno'wn' in the artifor producing a sawtooth waveform time ba'se'fo'r a cathode ray'tube(n'otsh'own); The output of the sweep generator is connected to the gridllilof cathode follower" tube V1. Thep'lateflfl of this cathode ro'nwertubeisconnected to a positive. po; tential, as shown Tl iecathode 1 3is'*connected through resistance 14 to a negative potential, as shown,and thrbngh the pa'rallel combination of resistance 'l and capacitor1640 the grid 17 of cathode follower V2. The'grid 17 is also connectedthron'gh'-= poterrtiometer 1 -8to"a nega tive 1 potential and to groundThis potentiometer fun'c tions to I vary the-voltage;- on grid-17,whereby topositior'ta desired part ofthe sweep o'rf-"thecat-l:1'ode-raytube screen.- Calhode follower V2 fi1n"ctions' to prevent grid currentfrom flowing in the cireuit of impedance- 15, 16?:

The pl'a'te 1-9 of tHbeNZ is connected=Fto a positive a tential, asshown, and the cathode 20 is connected through 2 resistance to anegative potential. The cathode 20 of tube V2 is also connected throughthe parallel combination of resistance 22 and capacitor 23' to the grid24 of cathode follower tube V3. The plate 25 of tube V3,

ode 29' of this tube is connected through potentiometer 30 to thecathode 31 of another amplifier tube V5, said cathodes 29 and 31 being'also connected through-the respective resistances 32, 33 to the negativepotential, as indicated. The grid 34' of tube V5 is grounded throughresistance 35. p a

The function of cathode follower tube V3 is to prevent grid current fromcharging the feedback network capacitor 213', thus avoiding longrecovery time. Potentiometer 30 functions as a degenerative controlbetween the cathodes 2.9 and 31 of the respective amplifier tubes V4 andV5 to act the magnification gain to the precise value desire e The plate56 of tube V4 is connected through resistance 37. to' a positivepotential, as shown, and also to the grid 38 of cathode follower tubeV6. The plate 39 of. tube V6 is connected to a positive potential andthe cathode i0 is connected through resistance 41 to ground. In similarmanner, the plate 420i tube V5 is connected through" resistance 43 to apositive potential and to the grid 44" of cathode follower tube V7. Theplate 45 of tube V7 is connected to the positive potential indicated andthe cathode'46' is connected through resistance 47 to ground.

The plate 36 of amplifier tube V4" is also connected through theimpedance comprising the' parallel combination of resistance 48 andcapacitor 49 and'through resistance 50 and. prot'entiometer' 51 to anegative potential, as shown, and through said potentiometer andresistance 52 t0 gIQund.

Potentiometer 51 functions to set the D. C. level of cathode followerftube V3 at the same level for both magnifying and normal positions, andis employed to adjust the partof thet'race which is magnified to centerthe latter upon the cathode-ray tubescreen.

Plate 36 is also connected through impedances 48, 49" andswitch 53 tothe' grid 24 ofcathode follower tubeV3. The switch is movable betweenthe MAG and- NORM positions and functions in-sucli manner that theamplifier operates at full gain when the switch is in the MACipositiomHowever, when the switchisin the NORM position a degenerative feedbacknetwork is placed between the plate 36 and grid- 28 0farnplifier tube-V4via the cathode follower V3. The value of resistance 22 and'capacitor'2-3 may be chosen to provide gain factors of any magnitude desired. Thegain may also be varied bychanging themagnitude of resistances 48and-50, but the former procedure-is I preferred.

Potentiometers 18 and 51 function in such'manner' as to equalize thepotentials-at junctions 54 and 55 while simultaneouslyadjustingthepotential at plate 36of amplifier tube v l to a value atwhich-the trace is presented at the'desired position on the cathode-raytube screen. In practice this potentialis preferably established tocenter the trace on the screen. In any event the trace is main tained atthe selected position on'the screen in both magn-ified andu'nma'gnifiedconditions since the potentials at terminals 54? and- 55'are' maintained equal.

The cathodes 46 and 46 of the respective cathode" foll'ower tubes-V6'and V7-a re connected to the deflection plate's D-of acathodeqaytubetnot shown). These cath' ode followers isolate thedeflection plate capacity from Patented June 26, 1956 the plate of theamplifier tubes and increases the bandwidth of the latter by a factor ofabout three times. The improved frequency response provides forincreased linearity of the sweep on the higher range.

The operation of the magnifying circuit described hereinbefore is asfollows: Let it be assumed that the ratio of resistances 48 and 22 is sochosen that the gain of amplifier tube V4 is reduced by a factor of fivewhen switch 53 is in the NORM position, as compared with the gain whenthe switch is in the MAG position. With the cathodes 40, 46 of theoutput cathode follower tubes V6 and V7, respectively, connected to thehorizontal deflection plates of a cathode-ray tube (not shown) andswitch 53 placed in the MAG position, potentiometer 18 is adjusted toset either the start or the end of the trace at the center of thescreen. Switch 53 is then moved to the NORM position and potentiometer51 is adjusted to bring the same part of the trace, i. e. the start orthe end thereof, at the center of the screen. Precise adjustment ofmagnification to exactly five times the normal time base is achieved byadjusting potentiometer 30, as explained hereinbefore.

Referring now to Figure 2 of the drawing, the sweep generator 59 outputis connected through the parallel combination of resistance 60 andcapacitor 61 to the grid 62 of cathode follower V8. The plate 63 isconnected to a positive potential, as indicated, and the cathode 64 isconnected to the cathode 65 of the diode connected tube V9. The grid 66and plate 67 are connected together and through resistance 68 to apositive potential. The cathodes 64 and 65 are connected throughresistance 69 to a negative potential, as shown.

The output of tube V9 is connected to the grid 70 of amplifier tube V10.The plate 71 of this amplifier tube is connected through resistance 72to a positive potential, and through the parallel combination ofresistance 73 and capacitor 74 to the grid 75 of cathode follower tubeV11. The plate 76 of cathode follower tube V11 is connected to apositive potential and the cathode 77 thereof is connected throughresistance 78 to a negative potential and through resistance 79 to thecontrol grid 80 of the output amplifier tube V12. The grid 75 of cathodefollower tube V11 is connected through resistance 81 to a negativepotential.

The grid 62 of cathode follower tube V8 is connected through resistances82 and potentiometer 83 to a negative potential and to ground, as shown.Horizontal positioning of the sweep on the cathode-ray tube screen isachieved by adjustment of potentiometer 83 which controls the negativevoltage return of the grid circuits of cathode follower V8 and amplifiertube V12.

The cathode 84 of amplifier tube V12 is connected to the cathode 85 ofthe cooperating amplifier tube V13, and also through variable resistance86 to a negative potential. This resistance functions to set thequiescent state current level of the coupled cathodes 84 and 85. Thegrid 87 of tube V13 is connected through the parallel combination ofvariable capacitor 88 and potentiometer 89 to ground and also throughpotentiometer 90 to a negative potential, as shown. The plate 91 ofamplifier tube V12 is connected through resistance 92 to a positivepotential and also to the grid 93 of cathode follower tube V14. Theplate 94 of this cathode follower tube is connected to a positivepotential and the cathode 95 thereof is connected through resistance 96to ground.

In similar manner, the plate 97 of amplifier tube V13 is connectedthrough resistance 98 to a positive potential and also to the grid 99 ofcathode follower tube V15. The plate 100 of tube V15 is connected to apositive potential and the cathode 101 thereof is connected throughresistance 102 to ground. The cathodes 95 and 101 of cathode followertubes V14 and V15, respectively, are connected to the horizontaldeflection plates D of a cathoderay tube (not shown).

A pair of switches 103 and 104 are connected, respectively, to the grid62 of cathode follower V8 and to the cathode 77 of cathode follower V11.These switches function to removably insert between them any one of aplurality of impedances comprising the parallel combinations ofresistance 105 and capacitor 106, resistance 107 and capacitor 108, andresistance 109 and capacitor 110. These impedances each complete adegenerative feedback network between the plate 71 and grid 70 ofamplifier tube V10, the network being formed through tubes V11, V8 andV9. The amount of feedback is determined by the voltage division of thevoltage divider comprising impedance 60, 61 and one of the switchedimpedances.

The function of cathode follower tube V8 is to prevent grid current fromflowing in the feedback network. Since the cathodes 64 and 65 areconnected together and since the plate 67 of the diode connected tube V9is connected to the grid 70 of amplifier V10, the plate 67 follows thegrid 62 of cathode follower V8 until grid current starts to flow inamplifier tube V10. At this time grid current flows through resistance68 to hold the diode plate 67 at a fixed voltage level while the cathoderises past it.

In the operation of the circuit shown in Figure 2, there is a value ofvoltage derived at the plate 71 of amplifier tube V10 at which thevoltages at junctions 111 and 112 are identical. Accordingly, thispotential will result in a certain output potential being positioned ata certain point on the screen, and this output potential will remain infixed position under all conditions of magnification provided by theswitched impedances. Potentiometer 90 may then be adjusted to shift theestablished potential to any desired position on the screen, for exampleto the center of the screen. As previously explained, the gain ofamplifier tube V10 may be adjusted by switching in any desired value ofimpedance into the feedback network when the potentials at terminals 111and 112 are equalized. For example, impedance 105, 106 may establish thenormal gain of the amplifier, While impedance 107, 108 increases thegain by a factor of three and impedance 109, increases the gain by afactor of ten. In this manner, a waveform to be analyzed may be viewedin its normal size or it may be magnified to three times or to ten timesits normal size. In all cases the waveform is maintained at the selectedposition on the screen.

By way of exemplifying the foregoing description, Figure 3 illustrates anormal size waveform 115 positioned at the exact center of thecathode-ray tube screen. This waveform is produced in the circuitry ofFigure 1 when switch 53 is in the NORM position and in the circuitry ofFigure 2 when impedance 105, 106 is inserted in the feedback networkdescribed hereinbefore. Waveform 116 is expanded to three times thenormal waveform and is produced by the circuit of Figure 2 by insertingimpedance 107, 108 in the feedback network, while waveform 117 ismagnified to five times the size of the normal waveform and is producedin the circuit of Figure 1 by switching switch 53 to the MAG position.The waveform 118, magnified to ten times the size of the normalwaveform, is produced by switching impedance 109, 110 into the feedbacknetwork of the circuit shown in Figure 2.

It will be observed from the foregoing description that in both of thecircuits of Figures 1 and 2 various magnifications are achieved byproviding a feedback network between theplate and grid of an amplifiertube and changing the impedance value of said feedback network tocorrespondingly vary the gain of the sweep amplifier.

It will be noted in the foregoing illustrations that magnification ofthe portion of the time base, and hence the portion of the waveform tobe analyzed, was described as being preferably effected at the center ofthe cathode-ray tube screen. However, it will be understood thatmagnification may be effected at any other place on the cathode-ray tubescreen, as may be desired.

Various other modifications and changes may be made in the details ofconstruction described hereinbefore without departing from the scope andspirit of the present 1. A method of magnifying a portion of a time;base:

on. a cathode-ray tube screen wherein the cathode'ray tube. includesdeflection platesand-an amplifier connecting the latter to a timebasesource,. said method.comprisingfeeding the amplifier output signal: backto the amplifier input, providing said feedback pathwithspaced points ofequal potential, and varying the impedance. between said spaced points,whereby to vary the gain. of the amplifier andcorresp ondingly magnifysaid portion of the time base.

2. A method of magnifying aportion of .a time base on acathode-ray tubescreeni wherein thecathode-ray tube includes deflection plates, and-anamplifier'connecting, the latter to-a time;base-source, saidmethodcoming feeding the amplifier output back to the amplifier. input,providing said feedback path with spaced points of equalpotential whenthe potential of the amplifier output is located at the desired positionon the cathoderay tube screen, and varying the impedance between saidspaced points, whereby to vary the gain of the amplifier andcorrespondingly magnify said portion of the time base.

3. In combination with a cathode-ray tube having deflection plates andmeansfor generating a time" base, means for magnifying a portion ofsaid'time base, said magnifying means comprising anelectron dischargeamplifying device having a cathode, a grid and a plate, cathode followermeans interconnecting the amplifying device and the time base generatingmeans and forming a feedback path from the amplifying device, spacedpoints in said feedback path, circuit means associated with said spacedpoints for establishing equal potentials at said spaced points,impedance means connected between said spaced points in the feedbackpath to vary the gain of the amplifying device and correspondingly varythe magnification of the time base, and means connecting the output ofthe amplifying device to the deflection plates of the cathode-ray tube.

4. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base,

means for magnifying a portion of said time base, said magnifying meanscomprising an electron discharge amplifying device having a cathode, agrid and a plate, a first cathode follower means interconnecting theamplifying device and the time base generating means and forming afeedback path from the amplifying device, spaced points in said feedbackpath, circuit means associated with said spaced points for establishingequal potentials at said spaced points, impedance means connectedbetween said spaced points in the feedback path to vary the gain of theamplifying device and correspondingly vary the magnification of the timebase, and second cathode follower means connecting the output of theamplifying device to the deflection plates of the cathode-ray tube.

5. The combination of claim 4 including a second electron dischargeamplifying device having a cathode and a plate, adjustable resistancemeans interconnecting the cathodes of the first and second amplifyingdevices, and third cathode follower means connecting the output of thesecond amplifying device to a deflection plate of the cathode-ray tube.

6. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base, means for magnifying a portion of saidtime base, said magnifying means comprising an electron dischargeamplifying device having a cathode, a grid and a plate, cathode followermeans interconnecting the amplifying device, and the time'basegenerating" means and forni ing afeedback path from thetamplifying,device, spaced points in said feedback path, circuit means associatedwithsaid spaced: points forv establishing equal potentials at saidspaced points, impedance means, switch means for removably inserting theimpedance means: between- I said spaced points in the feedback path,whereby to vary the gain of the amplifying device and correspondinglyvary the magnification of the time base, and means con meeting theoutput of the amplifying device to the de= flection plates of thecathode-ray tube.

7. In combination with a cathode-ray tube having,

deflection plates andmeans for generating a time base, means formagnifying a portion of said. time base, said magnifying meanscomprising an electron" discharge amplifying device having a cathode, agrid and a-plate,

cathode follower means interconnecting the amplifying-v device and thetime base generating means and form ing a feedback path from theamplifying device, spaced points in said feedback path, circuit meansassociatedwith said spaced points for establishing. equal potentials atsaid spaced points, impedance means connected. between said spacedpoints in the feedback pathto vary the gain of the amplifying device andcorrespondingly vary the magnification .of the time base, meansconnecting the output of the amplifying device to the dc flection platesof the cathode-ray tube, and adjustable resistance means between'thetime base generating means-v and the cathode follower interconnectingmeans for varying the position of the'magnified and unmagnifiedtirnebase on the cathode-ray tube screen.

8. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base, meansfor magnifying a portion ofsaidtime-base,- said magnifying means comprising an. electron dischargeamplifying device having a cathode, a grid and a plate,- cathodefollower means interconnecting the amplifying device and the time basegenerating means and forming a feedback path from the amplifying device,spaced points in said feedback path, circuit means associated with saidspaced points for establishing equal potentials at said spaced points,impedance means connected between said spaced points in the feedbackpath to vary the gain of the amplifying device and correspondingly varythe magnification of the time base, means connecting the output of theamplifying device to the deflection plates of the cathode-ray tube,adjustable resistance means between the time base generating means andthe cathode follower interconnecting means for varying the position ofthe magnified and unmagnified time base on the cathode-ray tube screen,and second adjustable resistance meansconnected to the amplifying devicefor adjusting themagnified and unmagnified time base at the sameposition on the cathode-ray tube screen.

9. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base, means for magnifying a portion of saidtime base, said magnifying means comprising an electron dischargeamplifying device having a cathode, a grid and a plate, first cathodefollower means interconnecting the amplifying device and the time basegenerating means and forming a feedback path from the amplifying device,spaced points in said feedback path, circuit means associated with saidspaced points for establishing equal potentials at said spaced points,impedance means, switch means for removably inserting the impedancemeans between said spaced points in the feedback path, whereby to varythe gain of the amplifying device'and correspondingly vary themagnification of the time base, second cathode follower means connectingthe output of the amplifying device to the deflection plates of thecathode ray tube, adjustable resistance means between the time basegenerating means and the first cathode cathode-ray tube screen, andsecond adjustable resistance means connected to the amplifying devicefor adjusting the magnified and unmagnified time base at the sameposition on the cathode-ray tube screen.

10. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base, means for magnifying a portion of saidtime base, said magnifying means comprising an electron dischargeamplifying device having a cathode, a grid and a plate, first cathodefollower means interconnecting the amplifying device and the time basegenerating means and forming a feedback path from the amplifying device,spaced points in said feedback path, circuit means associated with saidspaced points for establishing equal potentials at said spaced points,impedance means connected between said spaced points in the feedbackpath to vary the gain of the amplifying device and correspondingly varythe magnification of the time base, second cathode follower meansconnecting the output of the amplifying device to a deflection plate ofthe cathode-ray tube, adjustable resistance means between the time basegenerating means and the first cathode follower interconnecting meansfor varying the position of the magnified and unmagnified time base onthe cathode-ray tube screen, second adjustable resistance meansconnected to the amplifying device for adjusting the magnified andunmagnified time base at the same position on the cathode-ray tubescreen, a second electron discharge amplifying device having a cathodeand a plate, adjustable resistance means interconnecting the cathodes ofthe first and second amplifying devices, and third cathode followermeans connecting the output of the second amplifying device to adeflection plate of the cathode-ray tube.

11. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base, means for magnifying a portion of saidtime base, said magnifying means comprising an electron dischargeamplifying device having a cathode, a grid and a plate, cathode followermeans conductively interconnecting the amplifying device and the timebase generating means and forming a feedback path from the amplifyingdevice, means in the feedback path to vary the gain of the amplifyingdevice and correspondingly vary the magnification of the time base, andmeans connecting the output of the amplifying device to the deflectionplates of the cathoderay tube.

12. In combination with a cathode-ray tube having deflection plates andmeans for generating a time base, means for magnifying a portion of saidtime base, said magnifying means comprising an electron dischargeamplifying device having a cathode, a grid and a plate, cathode followermeans conductively interconnecting the amplifying device and the timebase generating means and forming a feedback path from the amplifyingdevice, impedance means, switch means for removably inserting theimpedance means in the feedback path, whereby to vary the gain of theamplifying device and correspondingly vary the magnification of the timebase, and means connecting the output of the amplifying device to thedeflection plates of the cathode-ray tube.

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